The concept of this hybrid dirigible glider intrigued me at first.One makes cyclical adjustments to the buoyancy of the winged dirigible by expanding and compressing the on-board helium, and with proper angle of attack control one induces forward flight. Elegant. http://www.fuellessflight.com.

Unfortunately, the inventor then goes further. He intends harvesting the energy required for re-compressing the helium by hanging out wind turbines during forward flight Um.. the forward flight is induced by compressing and expanding the helium and the forward flight allows wind turbines to comppress the helium?Argh.... another perpetual motion machine!

OK, so lets see if we do away with the fuelless part and salvage the hybrid dirigible-glider by adding a fuel driven aero-engine to power the substantial compressors that will be required. Yes.. we can, but now that we have fuel powered engines on board, we might as well connect them directly to propellers. And we can do away with the wings (that are propellers in a roundabout way) and we are back to and airship.

Hello, and welcome to forum, Warm Lug, and a great 2008 to all the members, contributors and readers of these pages.

You make an astute observation there re this concept for a self-propelled dirigible translating into nothing less than a PM machine. The proposed turbines and compressors are nowhere near 100% efficient mechanically and thermodynamically, something the inventor seems to have missed.

Another technical problem is with helium itself: the gas is so thin and chemically inert that it is difficult to contain and store for any length of time. The storage cylinders (made of iron or aluminium) have large wall thicknesses up to a few centimetres and a shelf life of only a few months. The reason for this is that the tiny helium atoms actually slip through the interatomic spaces of the cylinder wall and thus leak from the storage vessel. It is the same reason that a party balloon filled with helium stays inflated for about a day only. Of course, this problem plagues the compressor(s) also. Moreover, helium is rapidly becoming a scarce resource and costs a pretty penny.

... helium is rapidly becoming a scarce resource and costs a pretty penny.

Yes, tell me about it. My business is dependant on helium and the price is shocking.Ironically its the second most abundant element in the known universe. But then, bottled hydrogen isn't a whole lot cheaper.

The US used to have a federal monopoly on helium. The US still, as a nation, has a geographical lion's share of mineable helium (a virtual monopoly). Seems some natural gas fields in Siberia show promising amounts of helium. Mars, I read somewhere, could be the next best place to mine helium.

The situation is perhaps not as extremely dire as one might think. There’s a gas reservoir project going on in the Lindley, Free State, area which aims to exploit hydrocarbon gases, mainly methane, contained in and around a sequence of low-grade coal seams. The gas will be extracted via boreholes from surface and used for power generation.

There’s a fair amount of helium (a product of alpha-type radioactive decay) associated with the gas and it will be separated out, probably post-combustion, for use mainly as a primary heat-exchange medium for certain kinds of nuclear reactor.

A much closer source is Earth's moon. We have known for some time that the moon has loads helium-3 just lying around on the surface (a benefit of being blown by solar winds for billions of years). But at a concentration of 10 to 20 parts per billion we would have to set-up a processing plant on the moon or bring millions of tonnes of regolith back to Earth in order to make it a viable industry.

What does this mean for space development?

Well, according to the book "The Science Of Discworld" by Pratchett, Cohen and Stewart, this could be the "big project" that brings about the development of a space elevator (or more than one). The idea is to have a constantly rotating cable lifting loads into space and bringing loads down to earth. The equilibrium is important and you must bring down as much as you send up so that it only requires a small amount of a constant push to keep it going at a constant speed (this too is no perpetual motion machine - and "small" is relative to rocket ship engines performing the unaided task of lifting the loads). The space elevator would be bringing down millions of tonnes of valuable He-3 every day and sending-up everything from space station modules and spaceship parts to hazardous waste material. There are no estimates about when this could be done as nobody has announced plans along these lines. I think as individuals we may not see this become a reality in our lifetimes.